As is known in the art, chalcopyrite is a semiconductor, and therefore corrodes electrochemically in oxidizing solutions. In ferric sulphate media, the overall leaching reaction is as follows:CuFeS2(s)+2Fe2(SO4)3(a)→CuSO4(a)+5FeSO4(a)+2S0(s)
This reaction may be represented as a combination of anodic and cathodic half-cell reactions:Anodic half-cell reaction: CuFeS2→Cu2++Fe2++2S0+4e−Cathodic half-cell reaction: 4Fe3++4e−→4Fe2+
The fundamental problem with chalcopyrite oxidation is that the chalcopyrite mineral surfaces are passivated (i.e., they become resistant to electrochemical breakdown) at solution potentials above a certain level (generally considered to be about 550 to 600 mV vs Ag/AgCl). It is widely held that this results from the formation of some sort of passivating film on the mineral surface that most likely consists of an altered, partially Fe-depleted form of chalcopyrite. Because of this, most investigators have assumed that it is the anodic half-cell reaction (i.e., the mineral breakdown reaction) that limits the overall rate of leaching. It would be desirable to provide a leaching process in which such passivation is reduced.